Recent development in various media and high informatization in society have caused an abrupt increase in data traffic of mobile communications. This has made it difficult to supply sufficient data traffic only through communications (e.g., 2G communication, 3G communication, and LTE communication) using licensed spectrums (spectrums that are assigned to telecommunication common carriers or that are authorized or licensed to telecommunication common carriers).
In order to relieve such a situation, attempts have been made to partially offload data traffic through a Wi-Fi (registered trademark, the rest is omitted) communication, which uses an unlicensed spectrum, an unlicensed band, or an ISM band.
Non-Patent Literatures 1 and 2 each propose, as a technique for more efficiently utilizing an unlicensed spectrum, an LTE-U communication in which an LTE communication is made using an unlicensed spectrum.
The LTE-U communication is made so as to accompany an LTE communication (in the present specification, simply referred to as the “LTE communication”), which uses a licensed spectrum, and is used to partially offload downlink data traffic of the LTE communication with use of scheme such as a carrier aggregation or a supplemental downlink. It has also been considered to offload part of uplink data traffic of the LTE communication in the future.
The LTE-U communication is superior to the Wi-Fi communication in terms of, for example, the following points (1) through (3). (1) The LTE-U communication can share a wireless access network (and a core network) with the LTE communication. (2) Devices freely make communications during the Wi-Fi communication, whereas a more efficient communication is made by exchanging control signals via the LTE communication. (3) A device that makes the LTE-U communication less affects Wi-Fi devices than the Wi-Fi devices themselves affect each other. Meanwhile, the fact that there are many existing base stations (i.e., access points (AP)) is advantageous to the Wi-Fi communication.